Final answer:
Cestodes, or tapeworms, are adult segmented flatworms that live in the intestinal tract of their primary host. They do not have a digestive system and rely on their host for nutrients. The life cycle of tapeworms involves intermediate hosts and fertilized eggs.
Step-by-step explanation:
Cestodes, also known as tapeworms, are adult segmented flatworms that live in the intestinal tract of their primary host. Tapeworms have a long body composed of units called proglottids, which contain reproductive structures and detach when fertilized eggs are released.
These tapeworms do not have a digestive system but absorb nutrients from the host's intestine. The fertilized eggs are eaten by an intermediate host, where they develop into larval forms called oncospheres. When the intermediate host is eaten by the primary host, the cycle is completed.